As the Internet technologies are being developed, various buses have been widely applied to industrial field automatization, to monitor by a control end an industrial field in real-time, and there are different data transmission rates required in different application fields, where particularly the performance of servo systems, robots, and other systems requiring high precision may depend directly upon timely transmission of field data and control data, and there remains a bottleneck for the real-time performance of the existing buses.
In the prior art, data are transmitted over the Ethernet in a poorly real-time manner; and data are transmitted over the Ethernet in the mode of Carrier Sense Multiple Access with Collision Detection (CSMA/CD), so if the network is heavily loaded (more than 40%), then the deterministic network may not accommodate the real-time requirement of industrial control. There has been disclosed in the Invention Patent CN101778025B an apparatus and method for transmitting over the Ethernet at a transmission rate of the kilo-mega order, where the apparatus includes at least one single pair of differential line interfaces, and a two-wire Ethernet transfer device including a local transmitter and a local receiver coupled with the single pair of differential line interfaces, where the two-wire Ethernet transfer device communicates data in the mode of CSMA/CD collision detection, thus resulting in poorly real-time transmission in the system.
The operating characteristic and the operating mode of the CAN bus have been introduced in the paper “CAN BUS TECHNOLOGY AND ITS APPLICATION” published in “MANUFACTURING AUTOMATION”, where the event trigger mechanism of the CAN bus may cause events in the network to collide easily with each other, so that transmission over a channel may be subjected to an error and a jam, and even if the collision can be resolved by arbitration, then data transmission at a low priority may not be real-time; and if master and slave stations operate, then the respective nodes will communicate freely with each other by occupying a wider channel, thus lowering the transmission rate of the data over the channel, and consequently degrading the transmission performance. If the data are transmitted using the ID of a data packet, then the length of a message thereof will be so long that may result in a transmission delay, and although the data can be transmitted over a distance of up to 10 km, the transmission rate thereof will be significantly lower than the transmission rate over the Ethernet. There may be poorly real-time data transmission in the respective scenarios above.
Transmission of an EtherCAT message in an EtherCAT data frame has been disclosed in the paper “A STUDY ON INDUSTRIAL ETHERNET PROTOCOL BASED ON ETHERCAT” published in “Chinese Selected Master's Dissertation Electronic Journal”, where the data frame includes a legacy Ethernet frame, a message header, and other bytes, and there is an MAC address thereof for addressing, but the length of the message may be so long that may hinder the data from being transmitted rapidly, thus resulting in poor real-time transmission thereof.
In summary, the bus in the prior art may be poorly real-time, and a channel may be occupied for transmission, thus blocking the channel.